Sail Loading on Rig, Rig Loading on Vessel

Discussion in 'Sailboats' started by brian eiland, Oct 14, 2003.

  1. FAST FRED
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    FAST FRED Senior Member

    Then there is the crusing boat standard.
    Have he rigging sized so the weight of the boat can be lifted by any ONE wire.

    Sure its bigger than "racing designers" fancy , but when it gets 15 -20 years old and has stood 15-20 years of constant cycling loads (at anchor as well as underway) your "pucker factor" is greatly reduced in a blow.

    Offshore ,,2 wire redundancy is required ,
    in other words you should be able to snip ANY two wites and still have the mast stand.

    Sailors & boat builders ,, not racing designers opinion,

    FAST FRED
     
  2. MikeJohns
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    MikeJohns Senior Member

    Fred

    Your rig size guide would work on smaller boats, but things get a bit trickier when you have a large boat. I am just completing a rig design for a 40 tonne twin mast vessel. There is no way this would wear 40 tonne UTS cable, nor could you lose any two wires without losing the rig when under sail.

    People are often under the misconception that over-engineering is a good idea and from first looks it often appears so, but there are many other factors in a complex design and beefing up one part of the design simply causes another part to fail instead.

    For example You are better off with your rigging breaking than pushing the mast through the bottom of the boat or ripping out the chainplates (along with substantial amouts of hull).

    Also with rigs, over-engineering adds a large amount of mass at a distance detrimental to stability. Heavy rigs must be designed for on the drawing board.
     
  3. tonypearce
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    tonypearce Junior Member

    Pierre Gutelle Part II, Ch VI

    I have posted as an attachment;
    a Translation of Section 1, of Chapter VI, of Pierre Gutelle's work from "Design of Sailing Yachts" Part II.
    The translation was commissioned by myself at my expense. :rolleyes:
    This is a trial to see how the system works.
    Other sections of this work may be posted at a later time.

    Most of this work is common sense, but he does give a little insight into how the sails work in loading the mast and rigging. something that is missing from most other works. :cool:
     

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  4. water addict
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    water addict Naval Architect

    So you want a more "exact" method for rig design? If everyone who has contemplated the topic in the past has come up with such inadequate methods, why not create your own if you are so brilliant! If it ain't that complicated, then please - enlighten all of us!
     
  5. MikeJohns
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    MikeJohns Senior Member

    Water addict
    You need to say who you are targetting your comments at. Presumably not Tony Pearce for his effort to make a very good contribution to this thread.

    Tony
    Thankyou for posting that, I have had a quick glance at the pdf and it looks to be a thorough approach. I would like to see the rest.
    Perhaps some of us could make some $ contributions to you for the cost of the translation?

    Cheers
     
  6. water addict
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    water addict Naval Architect

    Mike,
    You are correct- my sarcasm is not directed at Tony, but at those who complain about current rig design procedures.

    Numerous folks, presumably at least some have looked into the issue, have posted that rig load and design is a very complex dynamics problem. Those who gripe that current methods are not up to their standards are free to create somthething better, and by all means distribute improved methods to the rest of us.

    Also, the complaint that rig loads are dependent upon righting moment and not sail force baffles me. Why would they not depend upon righting moment? Newtons 3rd-For every action there is an equal and opposite reaction. 0 RM = 0 rig forces. If there is no RM to react against, no forces would be transferred in the rig.
     
  7. brian eiland
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    brian eiland Senior Member

    Rig Loading chapter/discussions

    I'll second that motion....thanks VERY much. I've been away from the forum and didn't note the posting. As I told you in a private message, I'd be glad to contribute to your cost of translation. Again thanks a lot. I'll have a more thorough look at the material this weekend.
     
  8. brian eiland
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    brian eiland Senior Member

    .

    Dear Water Addict, it wasn't that I was so dissatisatisfied with the righting moment methods, it was a desire to really look at what was happening in all of the components of the rig....a mapping you might say. I'll repeat some of my original posting:
    I once read several articles from Chris Mitchell of Applied Engineering Services Limited (hi-lights) who hinted at this 'mapping of a rig' as well. I recently sent him an eMail and ask if he would join our discussion....hopefully.
     
  9. brian eiland
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    brian eiland Senior Member

    Rigging Loads to the Vessel

    Thanks Tony for that posting. Now can we go a bit further and see how Pierre Gutelle treats the subject of getting the rigging loads to the vessel??
    ________________________________
    I was looking thru some misc materials I had saved on the subject, and thought this might make an interesting addition to the thread. To give proper credit, this was contained in an article by Jim Taylor for a Feb issue of SAIL mag:

    Stresses, strains, and bent boats

    The primary loads on a typical sailboat hull result from having to resist not only the forces exerted below the waterline by a heavy ballast keel, but also those exerted above it by the mast and sails. These loads can often be measured in tons…many tons, in the case of an IACC boat. A how and arrow can he a useful illustration of the rig loads on a sailboat hull (Fig. 1). When the arrow (mast) is drawn back, the bow strings (headstay and backstay) are tensioned, and the bow (hull) bends. All boats with fore-and-aft rigging bend to some degree; the only question is how much. Starting with the rig relaxed, a stiff boat might have thousands of pounds of backstay tension and minimal headstay sag after swallowing 6 inches of permanent backstay length. A more flexible boat can swallow that same backstay length but can have a sagging headstay with jammed cabin doors, slack lifelines, and a shortened waterline.

    A boat’s hull and deck can also be viewed as a combination of I-beams loaded near mid-span (Fig. 2). The headstay and backstay pull up on the ends of the fore-and-aft beam, which is pushed down by the mast. In order for the I-beam to bend, its lower flange (the bottom of the hull) must get longer, while its upper flange (the deck) must get shorter. This means the lower parts of the hull will he stretched in tension, while the deck will he shrunk in compression. Because IACC boats have long, shallow hulls, the stresses in these flanges are even greater. There can also be stress concentrations where the decks are cut away to create optimum working areas for the crew.

    In the case of oneAustralia, my guess is that her hull failed under the tension, and it split wide open near the keel, causing her to sink like a stone. In contrast, it appears that USA 53’s deck failed in compression and that her hull bent dramatically but remained substantially watertight, allowing her to make it hack to the dock.

    Static verses dynamic loads

    A significant common denominator in those two IACC structural failures is that both occurred in choppy seas. The design community has a good working knowledge of the static rig and keel loads that a sailboat’s structure must bear, and it has sophisticated computer tools to model the stresses, strains, and load paths that those static forces generate. However, there are no comprehensive models for the additional dynamic loads that tall rigs, long, shallow hulls, and deep, heavy keels generate when slamming through waves. The various scantlings rules for offshore racers and empirical rules of thumb for cruisers account for these dynamic loads with arbitrary safety factors that are not based on any precise knowledge of how large these extra margins truly have to be—they are simply set high enough so that failures do not occur. The win-or-bust culture of IACC racing forces the designer to attempt to accurately quantify all of the loads, static and dynamic, in all the wind and sea conditions a boat may face. Unfortunately, bitter experience is still sometimes the best teacher.

    Is carbon the culprit?

    Absolutely not. In fact, the trickle-down of carbon-fiber composites from the aircraft industry has allowed a variety of lighter, stronger, stiffer solutions to boatbuilding problems. It is important to understand carbon’s strengths and weaknesses. A material’s properties can be characterized by locating it on a conceptual properties scale—with elastic-and-tough materials at one end and stiff-and-brittle ones at the other. Broadly speaking, elastic-and-tough materials deform relatively easily under load but can absorb a great deal of energy without failing. The materials at the stiff-and-brittle end of the scale do not stretch or compress as much under the same loads, but are not as forgiving in absorbing the energy of impact or shock loads.

    Over the past 25 years, the materials that make up all components of a sail— boat have undergone a dramatic shift from the elastic to the stiff end of the scale. This has set in motion a continuous 'find the weak link' design loop. This shift began when Dacron sails gave way to Mylar and Kevlar, exposing sheets and halyards as too stretchy. As running-rigging technology improved to keep up, deck hardware began to both march across the deck and come to pieces. When the decks were locally reinforced and the hardware was beefed up, flexible hull structures were exposed as inferior to stiffer ones. In each cycle around the loop, the use of stiffer, less-elastic materials has proved to be faster, but what has been lost is the shock-absorbing effect of all those previously elastic elements.

    Carbon-fiber composites definitely fall at the stiff-and-brittle end of the scale. They can be used to form exceptionally light and stiff structures, but they are not effective in absorbing shock loads. The micro-engineering required for a carbon laminate to withstand the readily quantifiable static loads is straightforward. The macro-engineering needed for them to with stand the less accurately known shock loads encountered in a seaway is geometrically more complex.

    The IACC structural failures do not mean that contemporary composite boats are globally suspect. The designers are not idiots, and the boatbuilders are doing a better job now than they have ever done. Scantlings rules have been very effective in promoting safety and maintaining reliability in the fleets that they control. The Americas Cup is simply a unique event that places a special premium on cutting-edge design development and technology with as few rules constraints as possible. These incidents show that we still have much to learn and that the process may he more difficult than we ever imagined.

    Jim Taylor has been creating racers and performance cruisers since 1978 from his design off/ice in Marblehead. Massachusetts.
     

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  10. MikeJohns
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    MikeJohns Senior Member

    Yes the statics are easy, its working out the allowances for accelerations of the vessel in a dynamic seaway that's nigh on impossible.
    Any engineering analysis for dynamics will have to be calculated from scratch for each and every vessel form and size. My associate (engineer) and I have attempted the dynamics but we fall back on the rules, liability issues also arise.

    Now if we took the vessel falling a certain distance onto a static water surface and dropped her from various angles and heights while also applying the static loads we may be able to come up with something like worst case dynamics.
    Then we could look at projected impact area, mass, deceleration coupled with the resultant righting moment and inertia and..............and you start to see what is involved, then its only for one hull form of a given mass.

    So you end up developing a few rules of thumb that can be applied to all vessels, and then you're right back where you started with rule based design.

    Nothing gauls an enginner more than not having some decisive numbers to design to !
     
  11. tonypearce
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    tonypearce Junior Member

    Gutelle Ch 6

    Season's Greetings,

    Please find the remainder of Pierre Gutelle's
    Chapter VI posted with this message

    Happy Reading
    Happy Christmas
    and a
    Rewarding New Year
    :D
     

    Attached Files:

    1 person likes this.
  12. brian eiland
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    brian eiland Senior Member

    Thanks Tony, I'll consider these one of my Christmas presents. Hopefully I'll read them some time tommorow after Santa has his visit.
     
  13. sorenfdk
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    sorenfdk Yacht Designer

    Tony:

    Thanks!!!
     
  14. MikeJohns
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    MikeJohns Senior Member

    Tony Pearce

    Well done and thank you very much, it will be very interesting to see his approach.

    You say you found one small error ?
     

  15. brian eiland
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    brian eiland Senior Member

    Structural Analysis of Yacht Rigs

    Chris was kind enough to send me some of his articles that he references on his website. I'm making my way thru them again.

    The first one that caught my attention was the one I had remembered seeing, that spoke to that same desire of mine to see a real 'computer mapping' of the rigging loads. He refers to this as a 'space-frame analysis', a "Computer Aided Analysis of Yacht Rigs", the subject of his Master's thesis at Univ of Auckland. In all fairness to him and his early thinking, I will add a qualifying statement that he includes with his presentation of these various subject articles, "I often wince at what I have written only a few years ago. It is either that I am getting smarter, or that everyone else has, and a bit rubbed off on me. Anyway, here is some stuff I have written, hopefully you may find them interesting".

    I find most of what he has written very interesting. So here is one of his early installments as a PDF document with some hi-lited portions that relate to the reasons I began this thread on the forum.
     

    Attached Files:

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